As a rotation sensing device capable of being incorporated into small-sized equipment and detecting an angle of rotation with high precision, a device utilizing a sensor arrays has been suggested (e.g. Japanese Laid-Open Patent Publication No. 2003-148999). This known device includes sensor arrays having a large number of arrayed magnetic sensor elements (MAGFET) integrated on a sensor chip together with a signal amplifying circuit, an analog-to-digital (A/D) converter circuit and a digital signal processing circuit, in which the sensor chip is arranged in face-to-face relation with magnetic generating means mounted on a rotatable member. With the rotation sensor of known structure discussed above, the magnetic sensor arrays detect distributions of magnetic fields generated by the magnet generating means, and from the distributions an angle of rotation of the magnet generating means are detected.
However, in a semiconductor circuit of the sensor, a thermal noise or a 1/f noise generated by the circuit is superimposed on output signals from the sensor elements integrated on a silicon chip, and therefore the accuracy of measuring the angle of rotation tends to be reduced.
Accordingly, there have been suggested: a device where the magnetic sensor elements in the above-mentioned sensor arrays are arranged in line to increase an effective area of the sensor and thus reduce the 1/f noise, so as to avoid the reduction of accuracy (e.g. Japanese Laid-Open Patent Publication No. 2004-037133); and a device where a plurality of magnetic sensor lines are arranged in parallel and each of the averages of outputs from sensor elements in the sensors line is calculated, so as to avoid the reduction of accuracy (e.g. Japanese Laid-Open Patent Publication No. 2005-043070).